Selectivity of geraniol synthase in aromatic species to control of cotton ramulosis

Abstract

Ramulosis (Colletotrichum gossypii South var. cephalosporioides Costa) is a fungal disease of cotton (Gossypium hirsutum L.) that causes damage to leaves, stems, and bolls by reducing fiber production; it can be controlled by chemical fungicides. Geraniol is a monoterpenoid produced by some aromatic plant species whose fungicidal properties have been widely reported. Geraniol synthase (GES; EC 3.1.7.11) is the precursor enzyme involved in the biosynthetic chain of geraniol. Geraniol synthase (ges) gene transcripts were prospected in 11 aromatic species with molecular and phytopathological tools to identify promising accessions for further use in in vitro and in vivo assays involving the control of cotton ramulosis. Mentha pulegium L. oil highly expressed ges and inhibited fungal growth at 1000 uL L-1 in an in vitro assay. Validation assays were carried out in two environments and M. pulegium at 2000 uL L-1 reduced the initial and final severity indices of the disease to 48% and 52%, respectively, in preventive treatments; in curative assays, indices were 44% and 54%, respectively. This indicates that it is a promising bioactive compound to control cotton ramulosis.